Because of the problem of destruction of the ozone layer in recent years, CFC (chlorofluorocarbon) and HCFC (hydrochlorofluorocarbon), which have been used as a refrigerant for refrigerating equipment until now, are subject to regulation, and HFC (hydrofluorocarbon) is being used as a refrigerant in place of them. However, HFC-134a, which is normally used as a refrigerant for car air-conditioner, among HFC refrigerants has an ozone depletion potential of zero but has a high global warming potential (GWP), and thus is subject to regulation in Europe.
The development of a refrigerant which has a little influence on the ozone layer and a low GWP is urgently needed against such background. Patent Literature 1, for example, discloses using a 1-chloro-2,3,3,3-tetrafluoropropene refrigerant from the viewpoint of, for example, a little influence on the ozone layer and a little influence on global warming.
In the meantime, a refrigerating machine oil containing a hydrocarbon oil such as mineral oil or an alkylbenzene has been favorably used when conventional CFC and HCFC are used as a refrigerant; however, refrigerating machine oils have unexpected behavior such as compatibility with a refrigerant, lubricity, viscosity of a solution with a refrigerant, and thermal and chemical stability depending on the types of coexisting refrigerant, and thus the development of a refrigerating machine oil for each refrigerant is required.